1. Field of the Invention
This invention relates to a grinding apparatus for grinding edges of metal strips, and more particularly to a grinding apparatus capable of mitigating uneven grinding due to unavoidable vibration in running of metal strips.
2. Description of the Prior Art
The term "metal strips" as used herein designates mainly band steels but is intended to include steel plates, die steels and the like whose edges are ground by rotating grinding wheels during running of the steels.
FIG. 1 illustrates one example of such a grinding apparatus which has been hitherto used. The grinding apparatus in FIG. 1 comprises a rotating grinding wheel 2 for grinding a metal strip 1, a motor 3 for driving the grinding wheel 2, a base or table 4 for supporting the grinding wheel 2, driving means 5 for forward and backward the table 4 toward and away from the edge of the strip, consisting, in this example, of a feeding screw, a motor 6 for rotatively driving the feeding screw and a nut threadedly engaged on the feeding screw and connected to the table 4, a load current detector 7 for the grinding wheel driving motor 3, and a constant-current control unit 8. A reference numeral 9 denotes a set value signal.
The FIG. 1 shows the apparatus for grinding by the rotating grinding wheel 2 an edge of the metal strip 1 running in a direction shown by an arrow .alpha.. The grinding power acting upon the grinding wheel 2 is identified with the load current of the grinding wheel driving motor 3.
In actual grinding, the table driving motor 6 is energized in a normal or reverse direction by the constant-current control unit 8 to move the table 4 toward and away from the edge of the metal strip 1 so as to bring the rotating grinding wheel 2 into contact with the edge of the metal strip in a manner the load current of the grinding wheel driving motor 3 is kept constant.
However, the metal strip in running is generally subjected to vibrations in longitudinal, traverse and vertical directions as shown by double-headed arrows in FIG. 1 to cause violent variation in load current of the grinding wheel driving motor 3. Accordingly, even if the grinding wheel supporting table 4 is operated so as to be advanced or retracted in response to the variation in load current of the grinding wheel driving motor 3 in the manner as above described, it does not match the great variation in load current resulting in an insufficient grinding power control.
As can be seen from FIGS. 2a, 2b and 2c which compare the load currents of the grinding wheel driving motor with respect to effect by forward and backward control of the grinding wheel supporting table, the constant-current control does not achieve its expected result. The edge of the metal strip is therefore unevenly ground to lower its worth as a product.